1. Technical Field
The present invention relates to methods for manufacturing ferroelectric memory devices having ferroelectric capacitors.
2. Related Art
Ferroelectric memory devices (FeRAM) are nonvolatile memory devices capable of low voltage and high-speed operation, using spontaneous polarization of ferroelectric material, and their memory cells can be each formed from one transistor and one capacitor (1T/1C). Accordingly, ferroelectric memory devices can achieve integration at the same level of that of DRAM, and are therefore expected as large-capacity nonvolatile memories. As the ferroelectric material, perovskite type oxides such as lead zirconate titanate (Pb (Zi, Ti) O3: PZT), and bismuth layered compounds such as strontium bismuth tantalate (SrBi2TaO9: SBT) can be enumerated.
A hydrogen barrier film that prevents reducing elements such as hydrogen from penetrating from outside is provided around a ferroelectric capacitor composing a ferroelectric memory device. The hydrogen barrier film prevents generation of oxygen deficiency in the ferroelectric material thereby preventing deterioration of electrical characteristics of the ferroelectric capacitor. Also, the ferroelectric capacitor is conductively connected to a wiring formed on an interlayer dielectric film covering the hydrogen barrier film through a plug formed in a contact hole that penetrates the hydrogen barrier film and interlayer dielectric film. For example, Japanese Laid-open Patent Application JP-A-2006-108269 is an example of related art.
The contact hole is formed, using a dry etching method. When the contact hole is formed in the interlayer dielectric film, a mixed gas containing, for example, CHF3 gas, CF4 gas and Ar gas may be used as an etching gas. When the contact hole is formed in the hydrogen barrier film, a mixed gas containing, for example, BCl3 gas and Cl2 gas as an etching gas.
However, the method for forming a ferroelectric memory device of related art entails the following problems. In the etching that uses the mixed gas containing BCl3 gas and Cl2 gas, a sufficient selection ratio cannot be obtained because the etching rate of an Ir film formed as a base layer of the hydrogen barrier film is high, which may lead to a problem of excessive cutting of the Ir film by over-etching.